The present invention relates generally to frequency transducers and more particularly to a frequency to voltage transducer for providing a voltage output signal proportional to the frequency of an input signal.
There are many instances in which it is necessary to provide a very accurate indication of the frequency of a signal. For example, in the discipline of electrical power generation, it is necessary to have an accurate indication of the frequency of the generated power so that the generating equipment can be controlled to maintain an accurate base frequency; e.g., 60 hertz (Hz). A number of systems have been devised for providing this function.
One of the more common methods of determining frequency, particularly with respect to power level signals, is to determine the times between zero crossings of the voltage signal being measured and to determine the frequency from those zero crossings. These systems can perform very well if the signal being measured is free of noise (or can be reconstructed so as to be free of noise) so that the zero crossings can be accurately determined. An example of a reconstruction technique suitable for use in the type of system just described can be found in U.S. Pat. No. 3,978,420 "Self-Tuning Filter" by L. Jubin Lane, issued Aug. 31, 1976, which patent is assigned to the assignee of the present invention and is specifically hereby incorporated hereinto by reference. This type of system is most applicable to those situations where the frequency variation is relatively large (e.g., 0 to 60 Hz) and where extreme accuracy is not required.
Such systems are not, however, particularly adapted for precise measurement centered around some critical frequency (e.g., 60.+-.0.5 Hz) such as required in the power generation industry. In addition, such systems normally require some additional means such as counters and evaluation circuitry to develop a suitable frequency control signal.